System for recovering glycol from glycol/brine streams

ABSTRACT

A system for recovering glycol from glycol and brine mixtures produced from oil or natural gas wells that combines energy efficiency with a capability for handling salt and other solids contained in the mixture. The system comprises three effect evaporator systems in series. Each effect evaporator system comprises an evaporator, a separator vessel, product pumps, and a solids removal system. 
     The process utilizes the system to remove salt and other solids as well as excess water leaving a glycol stream that can be reused as a hydrate inhibitor. The process begins by preheating a glycol/brine stream comprising approximately fifty percent (50%) glycol. The stream is then subjected to three evaporation cycles. The first evaporation cycle comprises introducing the preheated stream into a suppressed boiling point evaporator where the stream is heated under a constant pressure. The stream pressure is then dropped to cause a portion of the water contained in the stream to vaporize or flash. The flashing stream is then introduced into a separator vessel where the water vapor is separated from the remaining liquid stream. The water vapor is removed from the separator and condensed. The remaining liquid glycol/brine stream is then pumped from the separator vessel through a solids removal system where precipitated salts and solids are removed. These steps are repeated two additional times. Each time the remaining liquid stream becomes more concentrated with glycol until the finished product is approximately ninety percent (90%) glycol.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional of prior application Ser. No. 09/006,229 filed onJan. 13, 1998, now U.S. Pat. No. 6,023,003 which is hereby incorporatedby reference in its entirety for all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to glycol/water separation. Moreparticularly, the invention relates to a process and a system forrecovering glycol from glycol/brine streams produced from oil or naturalgas wells.

2. Description of the Related Art

A common problem associated with natural gas production is the formationof hydrates. Hydrates are solid compounds that form as crystals andresemble snow in appearance. They are created by a reaction of naturalgas with water, and when formed, they are about 10% hydrocarbon andabout 90% water. To prevent plugging of production lines and equipmentby hydrates, it is common to inject a hydrate inhibitor into the gaswell.

Traditionally, when producing gas offshore, methanol has been used as ahydrate inhibitor because it lowered the freezing point of water vaporand thus prevented hydrate formation in flow lines. The methanol wasproduced from the well along with the brine and the methanol/brinesolution was often disposed of by dumping it into the ocean.

More recently, economic and environmental considerations have forcedoffshore hydrocarbon producers to consider techniques for recoveringhydrate inhibitors from the inhibitor/brine streams. Processes thatrecover methanol from methanol/brine streams are known to those skilledin the art, however, there are disadvantages to these processes.Particularly, methanol recovery systems generally leave a large portionof the methanol in the brine stream that is lost during disposal.Therefore, the environmental problems associated with disposal of thebrine stream continue to exist. Additionally, some methanol is lostalong with the vapor phase. Because methanol is lost in the recoveryprocess, additional methanol must be purchased and transported to theoffshore platform to make up for the losses.

It has been known to use glycol as a hydrate inhibitor for natural gasstreams containing fresh water vapor. Glycol recovery systems are alsoknown to those skilled in the art to remove glycol from the glycol/waterstreams. Generally, these systems are designed to produce glycol/waterstreams having between about fifty (50%) and about ninety-five (95%)percent glycol.

As shown in FIG. 1, prior art glycol recover systems primarily consistedof a distillation column 10 in which the glycol was concentrated bydistilling off the accompanying water. A natural gas stream containingglycol and water was introduced into a series of separator vessels 12and 14 where the pressure was reduced to flash off the natural gas. Theglycol/water stream was then introduced into distillation column 10where it was heated by reboiler 16, typically a steam reboiler, to drivethe water overhead and concentrate the glycol. The recovered glycolstream produced by this process was approximately ninetynine percent(99%) glycol.

While glycol is an effective hydrate inhibitor for use with natural gaswells, the glycol recovery systems of the prior art are not particularlysuited for recovering glycol from glycol/brine solutions produced fromthe natural gas wells.

One significant problem with the prior art system of FIG. 1 is createdby the salt and other solids contained in the glycol/brine streams.Glycol/brine streams produced from natural gas wells typically containbetween about forty percent (40%) and about sixty percent (60%) glycol,about sixty percent (60%) and about forty percent (40%) water with aboutten percent (10%) to about twenty-five percent (25%) weight percentdissolved salt in the produced water. The distillation process oftenresults in precipitation of the salt that can foul and plug the recoverysystem.

Additionally, the prior art glycol recovery systems such as shown inFIG. 1 are extremely energy intensive. Distillation column 10 requires areboiler 16 to provide the heat necessary to drive off the water vapor.The heat duty required by the reboiler 16 is significant, approximately300 MM BTU's per hour for a nominal 5,000 barrels per day (“BPD”) glycolrecovery unit.

Thus, the need exists for an environmentally safe and energy efficientprocess for recovering hydrate inhibitors that are produced from oil ornatural gas wells along with a brine stream. Particularly, the needexists for a process that recovers glycol from glycol/brine streamsproduced from oil or natural gas wells that is less energy intensivethan the prior art systems and is not subject to fouling or pluggingproblems caused by salt and other solids in the stream. Additionally,the need exists for such a glycol recovery system that can be used onoffshore production platforms.

SUMMARY OF THE INVENTION

Briefly, the present invention is a process and a system for recoveringglycol from a stream of glycol and brine that has been produced from anoil well or a natural gas well. The present invention provides an energyefficient recovery process and system with capability for handling saltand other solids contained in the glycol/brine stream.

The system of the present invention comprises three effect evaporatorsystems in series. Each effect evaporator system comprises anevaporator, a separator vessel, product pumps, and a solids removalsystem. Triple effect evaporator systems have been known to thoseskilled in the art for concentration of other solutions, however, use ofsuch systems to recover glycol from glycol/brine streams is novel. Aparticularly novel feature of the system of the present invention is thecombination of a triple effect evaporator system with solids removalsystems. The solids removal systems can be a combination of ahydrocyclone and strainers, a continuous disk centrifuge, or othersolids removal systems known to those skilled in the art.

The process of the present invention is a novel process which utilizesthe triple effect evaporator system of the present invention to removesalt and other solids as well as excess water, leaving a glycol streamthat can be reused as a hydrate inhibitor. The process of the presentinvention begins by preheating a glycol/brine stream comprisingapproximately fifty percent (50%) glycol. The stream is then subjectedto three evaporation cycles.

The first evaporation cycle comprises introducing the preheated streaminto a suppressed boiling point evaporator where the stream is heatedunder a constant pressure. The stream pressure is then dropped to causea portion of the water contained in the stream to vaporize or flash. Theflashing stream is then introduced into a separator vessel where thewater vapor is separated from the remaining liquid stream. The watervapor is removed from the separator and condensed. The remaining liquidglycol/brine stream is then pumped from the separator vessel through asolids removal system where precipitated salts and solids are removed.

The above mentioned steps of introducing the stream into an evaporatorfor heating under pressure, dropping the stream pressure to cause aflash, separating the remaining liquid stream from the vapor stream,condensing the vapor stream, and pumping the remaining liquid streamthrough a solids removal system to remove salts and other solids arerepeated two additional times. Each time these steps are performed theremaining liquid stream becomes more concentrated with glycol and afterthe third cycle the finished product is approximately ninety percent(90%) glycol. To maximize the energy efficiency of the process of thepresent invention, heat energy from the water vapor generated in thethird evaporation cycle is used to supply heat for the secondevaporation cycle, and the heat energy from the second evaporation cycleis used to heat the first evaporation cycle. Additionally, heat from thefinished product glycol stream can be recovered and used during thepreheating step.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the invention can be obtained when detaileddescription set forth below is reviewed in conjunction with theaccompanying drawings, in which:

FIG. 1 is a process flow diagram of a prior art system usingdistillation to remove water from a glycol/water streams;

FIG. 2 is a process flow diagram of the process and the system of thepresent invention;

FIG. 3 is a process flow diagram of an embodiment of the solid removalsystem from the present invention utilizing a hydrocyclone incombination with strainers; and

FIG. 4 is an alternative embodiment of the solids removal system fromthe present invention utilizing a disk centrifuge.

DETAILED DESCRIPTION OF THE PREFERRED INVENTION

The present invention is a glycol recovery system and process for use onmixtures of glycol and brine produced from a hydrocarbon reservoirduring the production of natural gas. While the actual concentration ofglycol in the brine may vary depending upon production conditions,process of the present invention is preferably used to recover glycolfrom streams containing about fifty percent (50%) glycol and about fiftypercent (50%) brine. Typically, the stream will contain about thirteenpercent (13%) sodium chloride. However, those skilled in the art willrecognize that the process and the system of the present invention isequally applicable to glycol/brine streams of differing concentrations.Preferably, however the glycol brine streams are in the range of abouttwenty-five percent (25%) to about seventy-five percent (75%) glycol.

Additionally, the process and system of the present invention isapplicable to different types of glycol used as an hydrate inhibitorincluding ethylene glycol, di-ethylene glycol, and tri-ethylene glycol.However, the process conditions referred to herein refer to processesfor recovering tri-ethylene glycol.

When referring to process conditions herein, preferably the actualprocess temperature is within 15° F. of the stated process temperatureand the actual process pressure is within 10 psig of the stated processpressure. More, preferably, the actual process temperature should bewithin about 5° F. of the stated process temperature and the actualprocess pressure is within about 3 psig of the stated process pressure.Additionally, when referring to vacuum conditions, the actual processpressure is within 30 mm Hg of the stated process pressure.

Referring to FIG. 2, the process of the present invention begins bypreheating the glycol/brine feed stream. The degree of preheating isdependent upon temperature of the mixture as it is produced from thewell. Generally, this temperature will be approximately 40° F. However,the process of the present invention is equally applicable to mixturesproduced at other temperatures. Preferably, the glycol/brine feed streamis preheated in two stages to maximize energy conservation.

A first stage pre-heater 40, in conjunction with a second stage feedpre-heater 42, is used to preheat the feed stream from about 40° F. toabout 21° F. Preferably, first stage pre-heater 40 is a plate and frameexchanger such as is commonly known. Steam condensate from a firsteffect evaporator 102 can be utilized as the heat-source for first stagepre-heater 40. First stage pre-heater 40 generally heats the glycol feedstream to about 90° F.

Second stage feed pre-heater 42 further heats the glyco/brine feedstream after it exits first stage pre-heater 40. Preferably, secondstage pre-heater 42 is a shell and tube heat exchanger. The finalproduct glycol stream is utilized on the tube side of the exchanger asthe heat source for second stage pre-heater 42. This allows recovery ofthe heat energy from the glycol product stream that would otherwise bewasted by reinjection. Second stage preheater 42 heats the glycol/brinefeed stream to about 21° F.

As will be recognized, the preheating step is an optional step in theprocess of the present invention. However, preheating the feed streamdoes increase the energy efficiency of the process. It will also berecognized that the type and size of exchangers used for preheating canbe varied depending upon available stream temperatures and other designconsiderations commonly understood by those skilled in the art.Additionally, other heat sources available on a production platform maybe utilized as alternative heat sources for the preheating step.

After the step of preheating, the glycol/brine feed stream is introducedinto a triple effect evaporator system having a first effect evaporatorsystem 100, a second effect evaporator system 80, and a third effectevaporator system 50. The concept of triple effect evaporator systems iswell known to those skilled in the art, however, the system of thepresent invention has adapted the process for use recovering glycol fromglycol/brine streams. The system and the process of the presentinvention are particularly adapted to handle the salt and other solidscontained in the glycol/brine streams. Those skilled in the art willrecognize that the process and the system of the present inventionutilize a reverse feed arrangement. In a reverse feed arrangement themost concentrated solution of glycol/brine is at the highest temperaturein first effect evaporator system 100 and the lowest concentratedsolution is in the third effect evaporator system 50.

The evaporation process begins by introducing the feed stream into thethird effect evaporator 52. Preferably, third effect evaporator 52 is ashell and tube exchanger with titanium or monel tubes and a carbon steelshell. Additionally, evaporator 52 is a suppressed boiling pointevaporator such as is known to those skilled in the art. The feed streamis superheated in evaporator 52 to a temperature of approximately 210°F. while the boiling point is suppressed due to maintenance of a backpressure of approximately twenty-five (25) psig by back pressure controlvalve 54. The back pressure prevents boiling of the glycol/brine feedstream inside evaporator 52 which can result in fouling by the salt orother solids in the stream. Optionally, back pressure can be maintainedusing valves, piping restrictions, a restricting orifice, elevation, orother means known to those skilled in the art to maintain back pressure.

Next, the pressure of the stream is reduced as the stream is introducedinto third effect separator 56. As the pressure is dropped, thesuperheated feed stream boils and a portion of the water vaporizesinside separator 56. Separator 56 is a vessel capable of withstandingpressures of about 100 psig and also a full vacuum. Preferably,separator 56 has a cone bottom 150 to prevent precipitated salt ofsolids from accumulating inside separator 56. Separator 56 can bedesigned with multiple separation trays 152 to prevent glycol from beingcarried overhead with the water vapor.

Preferably, third effect separator 56 is operated under a vacuum toallow flashing at the lowest temperature possible. Typically, thirdeffect separator 56 will be maintained at approximately 140 mm Hg.

The remaining liquid glycol/brine stream is separated from the watervapor in separator 56. The water vapor exits separator 56 overhead andis condensed in condenser 62. Condenser 62 is preferably a shell andtube exchanger having titanium tubes and a 304 stainless steel shell.Sea water or water from a cooling tower can be used to remove heat incondenser 62.

The condensation of the water vapor creates the vacuum on the separator56. Additionally, ejector 64 assists in maintenance of a vacuum onseparator 56 by handling flow of any non-condensable vapors.

The remaining liquid glyco/brine solution is removed from separator 56by first effect product pumps 58 and pumped to solids removal system 60where salt and other solids precipitated solids are removed. Solidsremoval system 60 can be in the form of the embodiments discussed belowor any variety commonly known to those skilled in the art for removingsolids from process streams.

The concentration of the glycol/brine stream at this point in theprocess of the present invention is about 52% glycol and about 48%brine. Preferably, a large portion, about fifty percent (50%) or above,of the glycol/brine stream removed from separator 56 is recycled throughevaporator 52 along with the feed stream. Recycling of the glycol/brineincreases the heat transfer and decreases fouling as a result ofincreased velocity through the exchanger tubes. The remaining portion ofthe glycol/brine stream (“the 52% glycol stream”) is introduced into thesecond effect evaporator system 80 where the above steps are repeated.

The 52% glycol stream is introduced into second effect evaporator 82where it is heated from approximately 141° F. to approximately 238° F.under a pressure of about 2.6 psig. Second effect evaporator 82 is asuppressed boiling point evaporator of similar design to third effectevaporator 52. Pressure control valve 84 maintains back pressure on thestream as evaporator 82 superheats the stream. The pressure of thestream exiting evaporator 82 is reduced as it is introduced into secondeffect separator 86. Second effect separator 86 is of similar design asthird effect separator 56.

As the pressure is dropped on the stream exiting evaporator 82, it boilsand a portion of the water vaporizes inside separator 86. Typically,second effect separator 86 will be maintained at approximately 760 mm Hgor 0 psig.

The remaining liquid glycol/brine stream is separated from the watervapor in separator 86. The water vapor exits separator 86 overhead andis condensed in third effect evaporator 52 where it simultaneouslytransfers heat to the feed stream. As will be recognized, the recoveryof heat from the water vapor increases the energy efficiency of processof the present invention. The remaining liquid in separator 86 is pumpedout through second effect product pumps 88 and into solids removalsystem 90 for removal of precipitated salt and other solids. Solidsremoval system 90 is of similar construction to solids removal system60.

The concentration of the glycol/brine stream at this point in theprocess of the present invention is about 60% glycol and about 40%brine. Preferably, about fifty percent (50%) or above of theglycol/brine stream removed from separator 86 is recycled throughevaporator 82 along with the 52% glycol stream. The remaining portion ofthe glycol/brine stream (the 60% glycol stream) is introduced into firsteffect evaporator system 100 where the above steps are repeated.

The 60% glycol stream is introduced into first effect evaporator 102where it is heated from approximately 229° F. to approximately 344° F.under a pressure of about 30 psig. First effect evaporator 102 is asuppressed boiling point evaporator of similar design to third effectevaporator 52. First effect evaporator 102 is heated by a steam source,preferably 150 psig steam, which can often be supplied by waste heatfrom other processes. It will be recognized that in the preferredprocess of the present invention, the steam source to evaporator 102 isthe only heat energy added to the process. For an initial feed stream ofapproximately 10,000 barrels per day, approximately 56 MMBTU/hour ofheat energy is required. This compares to approximately 300 MMBTU/hourusing the prior art glycol/water concentration process of FIG. 1.

Pressure control valve 104 maintains a back pressure on the stream asevaporator 102 superheats it. The pressure of the stream exitingevaporator 102 is reduced as the stream is introduced into first effectseparator 106. First effect separator 106 is of similar design as thirdeffect separator 56. As the pressure is dropped on the stream exitingevaporator 102, it boils and a portion of the water vaporizes insideseparator 106. Typically, first effect separator 106 will be maintainedat approximately 15 psig.

The liquid stream is separated from the water vapor in separator 106.The water vapor exits separator 106 overhead and is condensed in secondeffect evaporator 82 where it simultaneously transfers heat to the 60%glycol stream. The condensed water vapors from each of the effectevaporator systems 50, 80, and 100 can be accumulated and disposed of bydischarging overboard or by other means.

The remaining liquid in separator 106 is pumped out through first effectproduct pumps 108 and into solids handling system 110 for removal ofprecipitated salt and other solids. Solids removal system 110 is ofsimilar construction to solids removal system 60.

The liquid solution after removal of any precipitated salts or solids isthe finished product of the process and the system of the presentinvention. The finished product stream is approximately ninety percent(90%) glycol. As discussed above, the finished product can be cooled insecond stage pre-heater 42 where it also serves as a heat source topreheat the feed solution. If desired, a portion of the 90% finishedglycol solution stream can be combined with the glycol/brine solutionproduced from the well to keep the feed steam concentrationapproximately constant at about fifty percent (50%) glycol and fiftypercent (50%) brine.

Several embodiments of the solid removal systems 60, 90, and 110 can beutilized in the present invention including various systems for removingsolids such as are commonly know to those skilled in the art. As shownin FIG. 3, one embodiment of the solids removal systems 60, 90, and 110is a combination of a hydrocyclone 70 and strainers 72. Each removalsystem 60, 90, and 110 is a separate stand alone system, however, asingle system will be described below.

Operation and design of hydrocyclones are known to those skilled in theart of solids filtration and removal. The glycol/brine solution ispumped by product pumps 58, 88, and 108 into hydrocyclone 70 where thesalts and other solids are separated by centrifugal force. The liquidforms a vortex inside hydrocyclone 70 and salt along with other solidsare dropped out an apex 76 at the bottom of hydrocyclone 70 as a slurry.Hydrocyclones acceptable for use with the present invention areavailable from Baker Hughes Process Systems as part of the Vortoilhydrocyclone separator series (specifically, M-5100-150#).

While hydrocyclone 70 can be used alone to remove solids from theglycol/brine streams, approximately 20% of the liquid stream pumped intohydrocyclone 70 will be lost along with the salt and other solids. Toavoid this result, precipitant accumulator 74 and strainers 72 can beused in series with the hydrocyclone to prevent the loss of liquidsolution. The solids containing slurry exits hydrocyclone 70 and flowsinto precipitant accumulator 74 where solids and salt are allowed tosettle on the bottom. The glycol solution flows out of accumulator 74and passes through strainers 72 where it is returned to the glycol/brinestreams.

Accumulated salt and solids in precipitate accumulator 74 can then beperiodically flushed out with water into strainers 72 where the salt andsolids are captured and the flush water is mixed back into the glycolstream. Preferably, precipitant accumulator 74 is a vertical cone bottomvessel that allows removal of accumulated salts. Accumulated salts canbe re-mixed with the condensed water from the effect evaporator systems50, 80, and 100 for disposal.

The hydrocyclone/strainer embodiment of solids removal systems 60, 90,and 110 has the advantages of requiring no moving parts, being lesssusceptible to plugging, and requires minimal shutdown time formaintenance. Disadvantage of this system include adding additional waterback into the process during the accumulator flush and the manualchanging and cleaning of strainers 72.

In addition to the embodiment of FIG. 3, solids removal systems 60, 90,and 110 can include continuous nozzle-disk centrifuges 120 (see FIG. 4),acoustic separators, or other means for removing solids as are commonlyknown in the art. An example of a continuous nozzle-disk centrifugeacceptable for use with the present invention is the Merco modelLPH-30-IN.

As can now be recognized, the present invention is a process and asystem for recovering glycol from glycol and brine mixtures producedfrom natural gas wells. The present invention provides an energyefficient recovery system with capability for handling salt and othersolids contained in the mixture. Additionally, the present invention isparticularly suited for use on offshore production platforms where spaceand energy conservation are important.

The foregoing disclosure and description of the invention areillustrative and explanatory thereof, and various changes in the detailsof the illustrated apparatus and construction and method of operationmay be made without departing from the spirit in scope of the invention.

What is claimed is:
 1. A system for recovering glycol from a glycol andbrine mixture produced from a hydrocarbon well, comprising: a firsteffect evaporator system comprising: a first heat exchanger for heatingthe glycol and brine mixture; a first pressure controller forcontrolling the pressure in said first heat exchanger while inducing apressure drop in the heated glycol and brine mixture; a first separatorvessel for receiving the heated glycol and brine mixture and separatingout vaporized water from the heated glycol and brine mixture to producea remaining glycol and brine mixture; and a first solids removal systemfor removing precipitated solids from the remaining glycol and brinemixture; and a second effect evaporator system comprising: a second heatexchanger for heating the remaining glycol and brine mixture; a secondpressure controller for controlling the pressure in said second heatexchanger while inducing a pressure drop in the heated remaining glycoland brine mixture; a second separator vessel for receiving the heatedremaining glycol and brine mixture and separating out vaporized waterfrom the heated remaining glycol and brine mixture to produce a moreconcentrated glycol and brine mixture; and a second solids removalsystem for removing precipitated solids from the more concentratedglycol and brine mixture; and a third effect evaporator systemcomprising: a third heat exchanger for heating the more concentratedglycol and brine mixture; a third pressure controller for controllingthe pressure in said third heat exchanger while inducing a pressure dropin the heated more concentrated glycol and brine mixture; a thirdseparator vessel for receiving the heated more concentrated glycol andwater mixture and separating out vaporized water from the moreconcentrated glycol and brine mixture to produce a concentrated glycolstream; and a third solids removal system for removing precipitatedsolids from the concentrated glycol stream.
 2. The system of claim 1further comprising a pre-heater before the first effect evaporatorsystem for pre-heating the glycol and brine mixture.
 3. The system ofclaim 2 wherein the pre-heater comprises two heat exchangers, a firstpre-heater exchanger and a second pre-heater exchanger.
 4. The system ofclaim 3 wherein the first pre-heater comprises a plate and frameexchanger for pre-heating the glycol and brine mixture using theconcentrated glycol stream.
 5. The system of claim 3 wherein the secondpre-heater comprises a shell and tube exchanger.
 6. The system of claim1 wherein the first, second, and third pressure controllers are selectedfrom the group consisting of valves, restricting orifices, pipingrestrictions, and piping elevations.
 7. The system of claim 1 whereinsaid separator vessels comprise vessels having cone shaped bottoms. 8.The system of claim 1 wherein said separator vessels further comprisesat least one separation tray per vessel.
 9. The system of claim 1wherein said first effect evaporator further comprises a condenser forcondensing the vaporized water separated by the first separator vessel.10. The system of claim 1 wherein: the first effect evaporator systemfurther comprises a first pump for pumping the remaining glycol andbrine mixture out of the first separator vessel and through the firstsolids removal system; the second effect evaporator system furthercomprises a second pump for pumping the more concentrated glycol andbrine mixture out of the second separator vessel and through the secondsolids removal system; and the third effect evaporator system furthercomprises a third pump for pumping the concentrated glycol stream out ofthe third separator vessel and through the third solids removal system.11. The system of claim 1 wherein each solids removal system comprises ahydrocyclone.
 12. The system of claim 11 wherein each solids removalsystems further comprise a strainer in series with the hydrocyclone. 13.The system of claim 12 further comprising an accumulator vessel foraccumulating solids removed by the hydrocyclone.
 14. The system of claim1 wherein each of the solids removal systems comprises a diskcentrifuge.
 15. The system of claim 14 wherein the disk centrifugecomprises a continuous nozzle disk centrifuge.
 16. The system of claim 1wherein each of the solids removal system comprises an acousticalseparator.
 17. The system of claim 1 wherein at least one of the solids,removal systems comprises a disk centrifuge.
 18. The system of claim 17wherein the disk centrifuge comprises a continuous nozzle diskcentrifuge.
 19. The system of claim 1 wherein at least one of the solidsremoval system comprises as acoustical separator.
 20. The system ofclaim 1 wherein at least one solids removal system comprises ahydrocyclone.